This invention relates to an apparatus and process for handling optical fibers and, more particularly, to a non-contacting guide for moving optical fibers.
Optical fibers are strands of glass fiber processed so that light transmitted therethrough is subject to total internal reflection. A large fraction of the incident intensity of light directed into the fiber is received at the other end of the fiber, even though the fiber may be hundreds or thousands of meters long. Optical fibers have shown great promise in communications applications, because a high density of information may be carried along the fiber and because the quality of the signal is less subject to external interferences of various types than are electrical signals carried on metallic wires. Moreover, the glass fibers are light in weight and made from a highly plentiful substance, silicon dioxide.
Glass fibers are fabricated by preparing a preform of glasses of two different optical indices of refraction, one inside the other, and processing the perform to a fiber. The optical fiber is coated with a polymer layer termed a buffer to protect the glass from scratching or other damage. As an example of the dimensions, in a typical configuration the diameter of the glass optical fiber is about 125 micrometers, and the diameter of the fiber plus the polymer buffer is about 250 micrometers (approximately 0.010 inches).
The fibers may be wound onto a cylindrical or tapered cylindrical bobbin with many turns adjacent to each other in a side by side fashion. After one layer is complete, another layer of fiber is laid on top of the first layer, and so on. The final assembly of the bobbin and the wound layers of optical fiber is termed a canister, and the mass of wound optical fiber is termed the fiber pack. When the optical fiber is later to be used, the optical fiber is paid out from the canister in a direction generally parallel to the axis of the cylinder.
The optical fiber that is recived from the manufacturer on a spool is carefully wound onto the bobbin during canister fabrication. Other processing of the optical fiber prior to its being wound onto the bobbin, for example various types of inspection, requires that the optical fiber be transferred from one spool to another spool. Thus, a good deal of handling of the optical fiber is often required. One key aspect of the handling is the guiding of the optical fiber from place to place in a manner that the optical fiber is stabilized against transverse motion, such as transverse vibrations that may develop when the optical fiber is transferred at a high linear rate of movement.
For such very fine optical fibers, the handling of the optical fiber to avoid damage that might introduce winding anomalies as the optical fiber is wound onto the bobbin or reduce its light transmission properties becomes an important consideration. Scratches, nicks, or adherent material on the buffer layer can cause irregularities during the precision winding of the optical fiber onto the bobbin, which then can lead to failure during high-speed payout. Damage to the buffer layer can cause surface damage to the glass, thereby lowering the tensile strength of the optical fiber. This produces an increased likelihood of failure of the optical fiber either before or during payout. Damage to the buffer layer or the glass light conductor can also reduce the fraction of light that is transmitted, and even slight reductions can be a serious concern if there are a number of such damaged places along the length of the optical fiber.
The presently utilized approach for guiding optical fibers and stabilizing them against transverse motion during linear movement is a mechanical pulley. The pulley is a wheel rotatably supported on a transverse shaft and having a flat or grooved rim against which the optical fiber bears. As the optical fiber is moved longitudinally, its movement is guided by passage over the pulley. The mechanical contact of the optical fiber to the pulley rim also damps transverse motion such as vibration.
Although the approach of using pulleys to guide strands of material as they move is well established, in the case of pulleys used with optical fibers there is a substantial risk that the mechanical contact between the pulley rim and the optical fiber buffer may induce damage in the optical fiber. Moreover, dirt and other foreign matter may accumulate in the grooved rim of the pulley. The dirt and foreign matter may either abrade the buffer surface at the point of contact with the pulley, or may be forced into the surface of the buffer layer at some location along the length of the optical fiber. The resulting irregularity may then interfere with the winding of the optical fiber onto the bobbin or result in irregular payout of the optical fiber from the canister at a later time. The irregularity can also be the source of a failure during service. Pulleys have the further disadvantage that the shaft bearings can become worn or dirty, increasing the drag on the optical fiber. The drag on the fiber increases the chance of mechanical damage to the buffer layer. If the drag is increased to a sufficiently large value, the optical fiber may break during transfer.
There is therefore a need for an improved system for guiding and stabilizing the motion of optical fibers as they are moved longitudinally. Such a system should be readily adaptable to a range of applications, and desirably is relatively inexpensive to implement. The present invention fulfills this need, and further provides related advantages.